Exciton interactions in synthetic porphyrin dimers

The Soret absorption spectra of six synthetic rigid porphyrin dimers whose crystal structures have been determined are simulated using simple exciton theory. The objective is to test the validity of the point dipole and associated approximations; the electronic interaction parameters are thus calculated using data obtained from the monomer spectra, with no adjustable parameters. Satisfactory agreement between theory and experiment is obtained for one class of dimers but not for a second. This poses a challenge for semiempirical electronic structure methods as to whether improvements over the point dipole calculations can be obtained.     

Some cytochemical studies on the cell surface ofAmphidinium carterae (Dinophyceae)

Summary The surface coat of the dinoflagellateAmphidinium carterae Hulburt was examined by fluorescence and transmission electron microscopy, using various fluorochromes and cationic dyes. The overall results showed cell-surface reactions typical of acid mucopolysaccharides. The cationic dye staining revealed an outer fine fibrillar layer (15–70 nm thick) overlying a dense anionic coat (40–60 nm thick) which appeared to thicken progressively with age. In general, the structure of the amphiesmal vesicles was similar to that previously described by other investigators. However, an acidic mucopolysaccharide layer was observed on the inner surface of these vesicles. Each of these structures is traversed by 1–3 pores and at least 2 types of extrusomes are formed, the spindle trichocysts and the mucocysts. Cell to cell adhesion through the surface coat was frequently observed. Evidence was also obtained for internalization of all the surface-coat markers used.This investigation forms part of a doctoral thesis submitted by the first author to the University of British Columbia, Vancouver, B.C.     

Induction of autolysis of staphylococci by the basic peptide antibiotics Pep 5 and nisin and their influence on the activity of autolytic enzymes

Pep 5 and nisin are cationic bactericidal peptides which were shown to induce autolysis in Staphylococcus cohnii 22. In contrast to nisin, Pep 5 induced lysis could be stimulated in the presence of glucose. Addition of lipoteichoic acids (LTA) (d-alanine:phosphorus=0.475:1) inhibited all effects of Pep 5 on susceptible cells in a molar ratio LTA:Pep 5 of 10:1. Treatment of S. cohnii 22 with Pep 5 or nisin for 20 min and subsequent washing with 2.5 M NaCl released autolysin activity. Crude preparations of the hydrolyzing enzymes produced free amino groups as well as polysaccharide fragments from the murein backbone, suggesting the presence of a muramidase or glucosamidase, and endopeptidase or amidase. Both enzyme activities were inhibited by lipoteichoic acid; they could be fully reactivated by addition of Pep 5 in sufficient concentrations. The velocity of hydrolysis was not influenced by nisin, whereas it was doubled in presence of Pep 5. The results are discussed in view of a possible mechanism of induction of lysis by Pep 5 and nisin.Abbreviations A.U. arbitrary unit - CCCP carbonylcyanide-m-chlorophenyl hydrazone - DNase deoxyribonuclease - CYG casein yeast extract glucose - IT initial turbidity - LTA lipoteichoic acid - RNase ribonuclease - TSB Tryptone Soy Broth     

Interference by DDT and cyclodiene types of insecticides with chloroplast-associated reactions

The effects of DDT, some of its analogs, and selected cyclodiene insecticides on isolated spinach (Spinacea oleracea L.) thylakoids were identified, characterized, and compared to responses induced by selected herbicides. Except for endrin, the insecticides inhibited light-induced electron transport, altered chlorophyll fluorescence transients, and competitively displaced [14C]atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], a known photosystem II inhibitor, from the membranes. The insecticides appeared to act at, or near B, the secondary electron acceptor of photo-system II. Binding of DDT and dieldrin was estimated at 900 and 2200 molecules, respectively, per photosynthetic unit (490 chlorophyll molecules). The insecticides also inhibited valinomycin-induced swelling of the thylakoid membrane. Whereas inhibition of electron transport can be attributed to interaction by the insecticides with a proteinaceous component of the thylakoid membrane, interference with the action of valinomycin may involve interaction with lipoidal constituents of the membrane.     

Accumulation of porphyrins and pyrrole pigments by Staphylococcus aureus ssp. anaerobius and its aerobic mutant

Abstract The anaerobic, Gram-positive coccus Staphylococcus aureus ssp. anaerobius and its aerobic mutant MVF-SR, when kept under anaerobic conditions, excreted coproporphyrin (mainly type III) into the medium and enriched uroporphyrin (mainly type I) within the cells.
The rate of porphyrin synthesis stayed practically unaltered when the growth medium was supplemented with 50 μ g/ml 5-aminolevulinic acid (ALA), but was significantly enhanced upon supplementation with hemin (0.5 μ g/ml). When hemin and ALA were given simultaneously, a more than two-fold increase in porphyrin production compared to normal growth medium was observed. These observations indicate a stimulation of porphyrin synthesis in S. aureus by hemin.
An as yet unidentified violet pigment with an intense red-violet fluorescence under UV light ( λ = 366 nm) was found to be present in considerable amounts in cells of S. aureus ssp. anaerobius , whereas the supernatant medium of aerobically grown cells of the mutant MVF-SR contained an equally unidentified blue, non-fluorescing pigment.     

L-lysine Transport in Chicken Jejunal Brush Border Membrane Vesicles

The properties of l-lysine transport in chicken jejunum have been studied in brush border membrane vesicles isolated from 6-wk-old birds. l-lysine uptake was found to occur within an osmotically active space with significant binding to the membrane. The vesicles can accumulate l-lysine against a concentration gradient, by a membrane potential-sensitive mechanism. The kinetics of l-lysine transport were described by two saturable processes: first, a high affinity-transport system (K _mA= 2.4 ± 0.7 μmol/L) which recognizes cationic and also neutral amino acids with similar affinity in the presence or absence of Na⁺ (l-methionine inhibition constant K_iA, NaSCN = 21.0 ± 8.7 μmol/L and KSCN = 55.0 ± 8.4 μmol/L); second, a low-affinity transport mechanism (K_mB= 164.0 ± 13.0 μmol/L) which also recognizes neutral amino acids. This latter system shows a higher affinity in the presence of Na⁺ (K_iB for l-methionine, NaSCN = 1.7 ± 0.3 and KSCN = 3.4 ± 0.9 mmol/L). l-lysine influx was significantly reduced with N-ethylmaleimide (0.5 mmol/L) treatment. Accelerative exchange of extravesicular labeled l-lysine was demonstrated in vesicles preloaded with 1 mmol/L l-lysine, l-arginine or l-methionine. Results support the view that l-lysine is transported in the chicken jejunum by two transport systems, A and B, with properties similar to those described for systems b ^0,+ and y⁺, respectively. Received: 14 August 1995/Revised: 2 April 1996     

Mechanism of aluminium-induced porphyrin synthesis in bacteria

In previous studies, aluminium was found to retard bacterial growth and enhance porphyrin formation in Arthrobacter aurescens RS-2. The aim of this study was to establish the mechanism of action of aluminium which leads to increased porphyrin production. Cultures of Arthrobacter aurescens RS-2 were incubated in the absence and presence of 0.74 mm aluminium. After 6 and 24 h of incubation, various parameters of the haem biosynthetic pathway were determined. After 6 h of incubation with aluminium, the activities of the enzymes aminolevulinate synthase (ALAS), aminolevulinate dehydratase (ALAD), porphobilinogen deaminase (PBGD) and uroporphyrinogen decarboxylase (UROD) were increased by 120, 170, 190 and 203%, respectively, while that of ferrochelatase (FC) was found to be unchanged. However, after 24 h of incubation, no change in the activities of ALAS and ALAD was noted, while an about 2-fold increase in PBGD and UROD activities were observed. FC activity was decreased by 63%. It was concluded that aluminium exerts its effect by inducing the enzymes PBGD and UROD rather than by a direct or indirect effect on ALAS. Its effect on the final step in the haem biosynthetic pathway is discussed.     

DNA immunization: Effects of vehicle and route of administration on the induction of protective antiviral immunity

Abstract The effectiveness of DNA immunization has been demonstrated in several model systems, usually following intramuscular injection of DNA in saline, or topical administration to the skin. In this study we have compared DNA delivered by three routes (intramuscular, intravenous, and intraperitoneal) and, for each route, in two vehicles (cationic liposome complex and pH sensitive liposome). These two lipid vehicles were evaluated because they are frequently used in gene therapy studies, but their immunogenicity has not been extensively studied. Each of these six combinations has been evaluated not only by assay of marker gene expression in a variety of tissues, but also by measurement of biologically-relevant parameters of immunity induction of antibodies, cytotoxic T lymphocytes, and protection against viral challenge. By both criteria (marker gene expression and induced immunity), the outcomes vary markedly among the six combinations. The combination leading to maximal marker gene expression (DNA with cationic lipid, administered i.v.) also induces detectable antibodies and CTL, and is the only one of the six combinations to induce immune responses comparable to those seen following i.m. injection of DNA in saline. However, marker gene expression can be detected in other combinations in the absence of induced immunity thus the value of marker gene expression in predicting the protection induced by a microbial antigen is questionable suggesting that, when evaluating various promoter constructs, marker gene expression may not adequately replace the direct measurement of biological outcomes.     

Cleavage of double-stranded DNA by manganese tris(methylpyridiniumyl)porphyrin linked to 3′-spermine oligonucleotides

 Cleavage of double-stranded DNA was performed with cationic manganese porphyrin complexes linked via a spermine tether to the 3′- or 5′-side of triple-helix-forming oligonucleotides (cleaver-TFO conjugates). The targeted sequence was a 15-polypurine sequence present in the env gene of HIV-1 (positions 7301–7315). The presently used TFOs contain only thymine and 5-methylcytosine residues and one adenine at the 3′-end in order to be able to easily introduce a 3′-polyamine linker by reductive amination of the corresponding 3′-apurinic polypyrimidine oligonucleotides. With this method we prepared these TFO-cleaver conjugates in 45% yield with only two equivalents of the Mn-TrisMPyP-COOH precursor. These new metalloporphyrin-TFO conjugates were able to cleave a complementary 45-mer duplex at 10 nM concentration with only ten equivalents of TFO-cleaver. Conjugates without spermine, without 5-methylcytosine, with a random sequence or with the managanese porphyrin-spermine entity on the 5′-end of TFOs were synthesized for comparative studies. Received: 6 December 1995 / Accepted: 5 February 1996